As is indicated by the name, F'lhaminn is a member of the F (bear) Seeker of the Sun tribe. However, as many of you have pointed out, she has many physical features which are attributed to Keepers of the Moon (such as iris shape, skin color, etc). As many of you have also noticed, there have been other characters which have displayed the features of one clan, while following the naming conventions of another. This can be attributed to two factors.
One: It could merely be a genetic anomaly. Just because certain races have a tendency to display certain features (pointed ears, long legs, darker or lighter skin, soul-piercing eyes), doesn't mean that once every thousand or ten thousand births, something deviates from the rules.
Two: It could be that a parent or grandparent was of a different clan, and the features of that clan were passed down. We know for certain that F'lhaminn was raised as a Seeker of the Sun, but we would have to look further down her family tree for clues why she has the appearance of a Keeper of the Moon.
Finally, some good news for our role-players who want a little more spice in their character's history--in character creation for ARR, we'll be allowing the mixing and matching of certain features between clans, so it will be possible to create a Keeper of the Moon-like Seeker of the Sun (or vice versa).